A typical Carrier Sense Multiple Access/Collision Detection (CSMA/CD) type fiber optic Local Area Network comprises a plurality of computers or stations connected together so that one station can communicate with another through a common bus. Specifically such networks are a configuration made up of a plurality of stations, each station being a combination transmitter and receiver and connected via transmitting and receiving optical fibers to a common bus, for example, a star coupler. At any given time, only one station can have access to the single channel of the system. Transmission by one station is a transmission to all stations through the star coupler. A problem faced by the prior art in this kind of a network arises out of the situation where more than one station is simultaneously transmitting, i.e., a "collision." When a collision takes place, it must be detected and dealt with, otherwise data packets will be lost, i.e., damaged beyond recognition. Current practice is to locate a collision detection means within the transmitter-receiver (transceiver) units. Signals that reach such collision detection means during a collision are not a single signal, but a mixture of two or more signals. Present day collision detection circuits rely on the assumption that this mixture of colliding signals has caused a detectible amount of distortion or abnormal signal and such can be detected because it is different from a normal signal.
In the context of Local Area Networks (LAN's) using fiber optic cable, this assumption is not always justified; for example, where one station is physically located nearer to the star coupler than another. Compare station 11 vs. station 12 or 4 of FIG. 1. The amplitude of a light signal diminishes as it travels through an optical fiber; thus, during a collision the signal from the station closest to the star coupler will be broadcasted to all other stations with a much stronger amplitude than the signal from a station further away. In such a situation, it is likely that the broadcasted mixed signals will look very much like the signal from the station closest to the star coupler. Stated in another way, the signal from the most remote station will be so weak compared to the signal from the closest station, their collision will fail to produce a detectible amount of distortion. A collision detection circuit based in the transceiver in the remote station will fail to detect the collision and this problem is known in the trade as the "dynamic range problem."